System &amp; method for preventing scaling in a flue gas desulphurization system

ABSTRACT

A system &amp; Method for Preventing Scaling in a Flue Gas Desulphurization System is provided. The system includes an injector configured to direct a barrier fluid toward a surface that is otherwise susceptible to scaling when it comes in contact with super-saturated alkaline solutions such as slurry used to capture CO2 from a flue gas stream.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to copending U.S. provisionalapplication entitled WALL SPARGER having ser. no. U.S. 60/895,268, filedMar. 16, 2007 which is entirely incorporated herein by reference.

FIELD OF THE INVENTION

The proposed invention is directed to preventing scaling in a flue gasdesulphurization system. More particularly, the proposed invention isdirected to preventing scaling and build up in an absorber tower of awet flue gas desulphurization system.

BACKGROUND

Fossil fuel fired boiler systems, such as those found and used inconjunction with, for example, electric power generation systemstypically expel exhaust by-products resulting from the combustion offossil fuel. This exhaust (or flue gas) often contains various chemicalcompounds, such as, for example, sulfur dioxide (SO₂) that are notdesirable for releasing into the atmosphere for general air flowdispersal. As a result, systems are provided to remove certain chemicalcompounds from the flue gas stream from a fossil fuel fired boilerbefore the flue gas is released into the atmosphere. Such systemsinclude, for example, wet flue gas desulphurization systems (WFGD) thatare configured to remove at least a portion of sulphur dioxide (SO₂)that may be contained in the flue gas stream, before it is released intothe atmosphere.

In wet flue gas desulphurization (WFGD) systems such as the one depictedin the diagram of FIG. 1, an absorber tower 50 is provided andconfigured to subject a flue gas stream (FG) to an alkaline slurry 130that captures at least a portion of SO₂ that may be present in the fluegas stream. The absorber tower 50 has an upper section 52 and a tanksection 55. The upper section 52 houses a plurality of spray heads 120configured to spray the slurry into the flue gas stream (FG) as itelevates through the upper section 52 to exit the absorber tower 50.Slurry is pumped to the spray heads from near the bottom of the tanksection 55 via one or more pumps 141, 142 and/or 143. As the flue gas FGcomes in contact with the slurry, SO₂ in the flue gas is captured by thealkaline slurry.

With reference to FIG. 1B and FIG. 1C, tank section 55 may be configuredto include a series of air outlets 112 for introducing air into theslurry contained in the tank section 55. This air is provided to helpspeed up the neutralization of SO₂ contained in the slurry. Each of theair outlets 112 is configured to include one or more orifices forreleasing air into slurry contained within the tank section 55. Theupward migration of these air bubbles occurs within the center portionof the tank section 55, away from the wall(s) 57. As a result the forceof the upward migrating air bubbles tends to push fresh slurry near thetop of the tank section 57 outward away from the center area of the tanksection 55 and toward the wall(s) 57. The migration of air bubbles andthe flow of fresh slurry is generally depicted in the diagram shown inFIG. 1D.

FIG. 1B is a diagram generally depicting the tank section 55 of theabsorber tower 50. In this example, the interior wall(s) of the tanksection 55 is not congested with accumulated scaling.

The example depicted in FIG. 1B and FIG. 1C shows a tank section 55 thatis configured to include a pipe grid 112 for introducing a gas, such asair, into the slurry contained in the tank section 55. Each of the airoutlets 112A-112E is configured to include one or more orifices 116 forreleasing air into slurry contained within the tank section 55. Theseair outlets 112 are provided to help evenly distribute the airthroughout the slurry as fine bubbles which travel to the liquid surfacethrough buoyant forces.

With reference to FIG. 1A and FIG. 1D the general function of the WFGDwill be discussed. After slurry is sprayed into the upper section 52 ofthe absorber 50 via the spray heads 120, the slurry comes into contactwith flue gas flowing through the absorber tower 50. This slurry makescontact with the flue gas and captures at least a portion of the SO₂that may be contained in the flue gas. This slurry with newly absorbedSO₂ (fresh slurry) falls downward toward and into the tank section 55.When the fresh slurry enters the tank section 52, the newly absorbed SO₂that is in the alkaline slurry is not yet completely neutralized. Untilthe SO₂ reacts with oxygen and calcium carbonate and forms a stablegypsum crystal, the solution may become supersaturated with respect toeither calcium sulfite or calcium sulfate. In this supersaturated state,the solution is prone to cause scaling to occur on interior surfaces ofthe tank section 55.

With reference to FIG. 1A, FIG. 1D & FIG. 1E, the fresh slurry residesin the tank section 55 until it is pumped out or re-circulated bycirculation pump 141, 142 & 143 back to the spray heads 120 in the uppersection 52. While in the tank section 55, the fresh slurry eventually,over time, migrates downward toward the bottom of the tank section 55.By the time fresh slurry reaches near the bottom of the tank section 55,the solution approaches equilibrium and thus the slurry is no longer assaturated as when it first entered the top of the tank section (as freshslurry). Thus, this “aged slurry” tends to be less likely to react withthe interior wall of the tank section 55 and, as a result, does generalresult in the build up of much, if any, scaling on the interior wall.

FIG. 1E is a diagram depicting the tank section 55 after scaling 65 hasaccumulated on the interior wall 57. FIG. 1E is a diagram depicting apartial cut-away view of the tank section 55 after scaling 65 hasaccumulated on the interior wall 57.

With reference to FIG. 1E and FIG. 1F, in the absorber tower 50, it iscommon for scaling to occur and accumulate along the interior wall(s) 57of the absorber tower 50 due to the supersaturated nature of the slurryfreshly subjected to the flue gas stream (fresh slurry). This scalingtypically occurs in and around the tank section 55 of the absorber tower50; however it is not limited to this area alone.

From time-to-time, accumulated scaling must be removed from the absorbertank wall(s). In order to remove the scaling, it is typically necessaryto shut down the WFGD system 25 and manually enter the absorber tank 50to physically remove the scaling from the walls(s). This often requiresthe set up and subsequent removal of equipment, such as, for example,scaffolding and safety equipment within the interior of the absorbertank to allow personnel to reach areas on the absorber tank interiorwall where scaling has occurred and safely remove it.

Shutting down the WFGD, as well as setting up systems for personnel touse in removing the scaling from the interior walls is a time consumingand expensive endeavor. Further, introducing personnel into the enclosedspace of the absorber tank subjects them to potential safety risksassociated with scaling falling from the interior walls.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a system and method forreducing scaling in a flue gas desulphurization system. Brieflydescribed, in architecture, one embodiment of the system, among others,can be implemented as follows. There is provided an injector configuredto be placed into a tank section of an absorber tower. The injector isfurther configured to direct a fluid into slurry within the tank sectionso as to push aged slurry toward an interior wall of the tank section.

Embodiments of the present invention can also be viewed as providingmethods for scaling in a flue gas desulphurization system. In thisregard, one embodiment of such a method, among others, can be broadlysummarized by the following step of: placing a non-super saturatedslurry against an interior surface of an absorber tower.

Other systems, methods, features, and advantages of the presentinvention will be or become apparent to one with skill in the art uponexamination of the following drawings and detailed description. It isintended that all such additional systems, methods, features, andadvantages be included within this description, be within the scope ofthe present invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood and its numerous objectsand advantages will become apparent to those skilled in the art byreference to the accompanying drawings in which:

FIG. 1A is a diagram generally depicting a typical flue gasdesulphurization system 25.

FIG. 1B and FIG. 1C are diagrams generally depicting a typical gasoutlets 112.

FIG. 1D is a diagram generally depicting the migration and flow ofslurry 130 from top to bottom in the tank section 55.

FIG. 1E and FIG. 1F are diagrams generally depicting scaling that occursalong the interior wall 57 of the tank section 55 of the absorber tower50.

FIG. 2 is a diagram generally depicting an embodiment of the proposedinvention in which a gas injector 225 is provided.

FIG. 3A-FIG. 3C are diagrams generally depicting a possibleimplementation of injector 225.

FIG. 3D is a diagram generally depicting an example of a possibleconfiguration of the absorber tower 50 wherein more than one injector225 is provided near the bottom of the tank section 55.

FIG. 3E-FIG. 3F are diagrams generally depicting examples of possibleconfigurations of orifices 230 on the injector 225.

FIG. 3G-FIG. 3H are diagrams generally depicting examples of possibleconfigurations of nozzles 320 that may be used in conjunction with theinjector 225.

FIG. 4 is a diagram generally depicting the flow of aged slurry as it isforced from near the bottom of the tank section 55 upward toward andagainst the interior wall 57 of the tank section 55 by air emitted fromthe apertures 230 of the injector 225.

FIG. 5 is a diagram generally depicting a further embodiment of theproposed invention in which aged slurry from the near the bottom of thetank section 55 is provided to the injector 225 and ejected so as toforce aged slurry toward and against the interior wall 57.

DESCRIPTION OF INVENTION

The proposed invention is directed to a system and method for keepingslurry rich with SO₂ (fresh slurry) away from the walls of the spraytower 50 by placing a barrier between the fresh slurry and the wall(s)of the tank section 55 of the spray tower 50. By keeping the freshslurry, which is still highly supersaturated, away from the absorbertower walls, scaling and build-up along the interior surfaces of theabsorber tower 50 is greatly reduced, if not eliminated.

In one embodiment of the proposed invention, the barrier is created byforcing aged slurry resident near the bottom of the tank section 55, andthat is no longer highly reactive, from the bottom of the tank section55 upward and against the inside perimeter of the wall(s) of the tanksection 55. The aged slurry may be forced from near the bottom of thetank section 55 by various means.

FIG. 2 is a diagram generally depicting an embodiment of the proposedinvention. In this embodiment, the absorber tower 50 is provided withone or more injectors 225 configured to spray a fluid, such as air, in adirected manner that causes aged slurry located near the bottom of thetank section 55 to be pushed or lifted upward and against the wall 57 ofthe tank section 55.

FIG. 3A-FIG. 3C are diagrams generally depicting a possibleimplementation of the injector 225. In this example, the injector system225 is configured to spray a fluid, such as air, upward toward theinterior wall 57 of the tank section 55. The injector 225 is preferablya hollow tube-like conduit having an interior cross section of a givenlength. The injector 225 is generally ring shaped and has a diameterthat is less than the diameter or cross-section of the tank section 55,although it is completely possible to configure injector 225 in othershapes to best provide coverage of the interior tank section 55 wall 57.The injector 225 is further configured to provide one or more apertures230 for allowing a fluid pumped into the injector 225 to be released ina given direction and in a given pattern of dispersion. The number ofapertures disposed along the injector 225 are contingent upon, amongother things, the extent of desired coverage of the interior wall 57surface.

FIG. 3E and FIG. 3F are diagrams generally depicting a possibleconfiguration of apertures 230. In the example shown in FIG. 3C, theaperture 230 is generally circular or elliptical in shape. In theexample shown in FIG. 3D, the orifice 230 is generally square orrectangular in shape.

With reference to FIG. 3G and FIG. 3H, the injector 225 may beconfigured to include one or more nozzles 320 fitted to the injector 225via one or more of the apertures 230 (not shown). These nozzles may beprovided to better direct (or aim) fluid output to control the flow ofaged slurry against the interior wall 57 (FIG. 2) of the tank section 55(FIG. 2) in a desired direction and in a desired dispersal pattern tooptimize coverage of the interior wall 57 or regulate output pressure ofthe released air/gas.

FIG. 4 is a diagram generally depicting the flow of aged slurry as it isforced from near the bottom of the tank section 55 upward toward andagainst the interior wall 57 of the tank section 55 by air emitted fromthe apertures 230 of the injector 225. It can seen that the aged slurryforced upward and against the wall acts as a barrier between thefresh(er) slurry resident toward the upper regions of the tank section55 and the interior wall 57 of the tank section 55.

FIG. 5 is a diagram depicting a further embodiment of the presentinvention in which the fluid output from the injector 225 isnon-saturated slurry (aged slurry) re-circulated from near the bottom ofthe tank section 55. In this embodiment, aged slurry is pumped via pump544 from near the bottom of the tank section 55 and injected into theslurry via the injector 225.

It should be noted that, if desired, the injector 225 may be configuredto work simultaneously with, or otherwise in conjunction with, a systemof gas outlets 112. Both the injector 225 and a system of gas outlets112 may be provided if desired.

It should be emphasized that the above-described embodiments of thepresent invention, particularly, any “preferred” embodiments, are merelypossible examples of implementations, merely set forth for a clearunderstanding of the principles of the invention. Many variations andmodifications may be made to the above-described embodiment(s) of theinvention without departing substantially from the spirit and principlesof the invention. All such modifications and variations are intended tobe included herein within the scope of this disclosure and the presentinvention and protected by the following claims.

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 12. A method of controlling scaling in a flue gasdesulphurization system comprising: directing an alkaline fluidoutwardly from an injector in a tank section of an absorber toweragainst side interior walls for alkaline fluid contact therewith; andforming an aged alkaline slurry barrier on the side interior walls byalkaline fluid movement of aged alkaline slurry upwardly toward and intocontact with the side interior walls reducing scaling thereon.
 13. Themethod of claim 12 wherein the injector comprises a hollow conduit inwhich a plurality of apertures is provided.
 14. The method of claim 12wherein the injector is generally ring-shaped.
 15. The method of claim12 wherein the injector further comprises spray nozzles fitted to saidapertures.
 16. The method of claim 12 wherein the injector comprises aplurality of apertures fitted with nozzles configured so as to directalkaline fluid into aged alkaline slurry moving the aged alkaline slurrytoward and against the side interior walls of the tank section formingan aged alkaline slurry barrier there against.
 17. The method of claim12 wherein the alkaline fluid comprises a gas.
 18. The method of claim12 wherein the alkaline fluid comprises air.
 19. The method of claim 12wherein the alkaline fluid comprises a non-supersaturated alkalineslurry.
 20. The method of claim 12 wherein the aged alkaline slurrycomprises an alkaline slurry not supersaturated with calcium sulfite orcalcium sulfate.
 21. The method of claim 20 wherein the aged alkalineslurry is re-circulated from near the bottom of the tank section.